The origin of languages was a hotly debated topic in the eighteenth century. This paper reconstructs a distinctively Kantian account according to which the origination, progression, and diversification of languages is at bottom reason’s self-development under certain a priori constraints and external environments. The reconstruction builds on three sets of materials. The first is Herder’s famous prize essay on the origin of languages. The second includes Kant’s explicit remarks about language – especially his notion of “transcendental grammar,” his argument that language cannot be innate, his contrast of “Oriental” symbolic (intuitive) and “Occidental” discursive languages, and his treatment of the latter as a sine qua non of humanity’s cultural and moral progress. The third includes the concepts that we need to make sense of those remarks, such as Kant’s epigenetic theory of biological formation and his account of categories as originally acquired.